Chlorobenzene isomers

Des Rosiers PE, Lee A. 1986. PCB fires Correlation of chlorobenzene isomer and PCB homolog contents of PCB fluids with PCDD and PCDF contents of soot. Chemosphere 15 1313-1323. 

The limited data from both in vitro and in vivo assays for chlorobenzene isomers other than 1,4-di-chlorobenzene indicates that chlorobenzenes are not mutagenic. 

The electron affinities of the chlorobenzene isomers have been determined by scaling half-wave reduction potentials [22], With higher gas phase values higher values are obtained from reduction potentials. These are compared to the ECD and CURES-EC values in Table 11.9. The CURES-EC-calculated values for the above compounds support experimental quantities and suggest that the Ea of all halogenated benzenes can be calculated. The CURES-EC values are listed in Table 11.10. The Ea... 

Typical enrichment of organic chemicals in the aquatic food chain of Lake Ontario has been observed for DDT and PCBs, which exhibit concentrations up to 8 ug/g and 17 tg/g, respectively, in fish on a lower concentration level - mainly due to the higher solubility of these compounds - similar effects can be seen for mirex and lindane (Table 2-8). Chlorobenzenes, in relation to sediment data, do not exhibit food chain enrichment, except for hexachlorobenzene, which is significantly concentrated in planktonic and benthic organisms. However, there is a distinct accumulation of all chlorobenzene isomers by organisms from the water phase, and it has been Stressed by Oliver Nicol (1982) as a typical feature that Lake Ontario fish contains much higher concentrations of CB s than fish from the other Great Lakes. 

M.p. I08-5 C. Ordinary DDT contains about 15% of the 2,4 -isomer, and is prepared from chloral, chlorobenzene and sulphuric acid. It is non-phytotoxic to most plants. It is a powerful and persistent insecticide, used most effectively to control mosquitoes in countries where malaria is a problem. It is stored in the bodies of animals and birds. 

The commercial product, m.p. 53-55°, may be used. Alternatively the methyl -naphthyl ketone may be prepared from naphthalene as described in Section IV,136. The Friedel - Crafts reaction in nitrobenzene solution yields about 90 per cent, of the p-ketone and 10 per cent, of the a-ketone in carbon disulphide solution at — 15°, the proportions ore 65 per cent, of the a- and 35 per cent, of the p-isomer. With chlorobenzene ns the reaction medium, a high proportion of the a-ketone is also formed. Separation of the liquid a-isomer from the solid p-isomer in Such mixtures (which remain liquid at the ordinary temp>erature) is readily effected through the picrates the picrate of the liquid a-aceto compound is less soluble and the higher melting. 

The isomer proportions for the nitration of the chlorotoluenes, to be expected from the additivity principle, have been calculated from the partial rate factors for the nitration of toluene and chlorobenzene and compared with experimental results for nitration with nitric acid at o °C. The calculated values are indicated in brackets beside the experimental values on the following structural formulae. In general, it can be... 

Chlorine and bromine add to benzene in the absence of oxygen and presence of light to yield hexachloro- [27154-44-5] and hexabromocyclohexane [30105-41-0] CgHgBr. Technical benzene hexachloride is produced by either batch or continuous methods at 15—25°C in glass reactors. Five stereoisomers are produced in the reaction and these are separated by fractional crystallization. The gamma isomer (BHC), which composes 12—14% of the reaction product, was formerly used as an insecticide. Benzene hexachloride [608-73-17, C HgCl, is converted into hexachlorobenzene [118-74-17, C Clg, upon reaction with ferric chloride in chlorobenzene solution. 

Dichlorobenzene is sold as two grades technical chlorobenzene <0.05, trichlorobenzenes <1.0, 1,2-dichlorobenzene 80, and other isomers <19.0 and purified, produced by redistilling the technical product in a very efficient stiU chlorobenzene <0.05, 1,2,4 trichlorobenzene <0.2 and 1,2-dichlorobenzene 98.0. 

The nitration of nitrobenzene and of chlorobenzene are known to occur via the same mechanism the ring is initially attacked by NO2, yielding a cation intermediate for each isomer. When the nitration process is fully complete, the distribution of the various isomers of the final product varies greatly for the two compounds ... 

A p-PhS02 group enhances the electrophilic reactivity of chlorobenzene towards KOH far more than a p-PhSO group, and the p-isomer is much more reactive than the m-isomer in each group. 

A variety of other reactions such as acylation of toluene, anisole, and chlorobenzene to give selectively p-isomer, alkylations, etc. have been conducted with IL. 

Zimmerman and co-workers were also able to obtain some information regarding the multiplicities of the excited states responsible for the initial /9-cleavage through quenching and sensitization studies. It was found that both trans-to-cis and cis-to-trans isomerizations could be sensitized by chlorobenzene under conditions where the latter absorbed over 95% of the light. The same product ratio was obtained under these conditions as in the direct irradiation of the ketones. With 1,3-cyclohexadiene or 2,5-dimethyl-2,4-hexadiene as quenchers nearly 90% of the reaction of the trans isomer could be quenched. Again the ratio of the quenched reaction products was the same as in the unquenched reaction. The reaction of the cis isomer, on the other hand, could not be quenched by 1,3-cyclohexadiene or 2,5-dimethyl-2,4-... 

Meso- and (+ )-azobis[6-(6-cyanododecanoic acid)] were synthesized by Porter et al. (1983) as an amphipathic free radical initiator that could deliver the radical center to a bilayer structure controllably for the study of free radical processes in membranes. The decomposition pathways of the diazenes are illustrated in Fig. 36. When the initiator was decomposed in a DPPC multilamellar vesicle matrix, the diazenes showed stereo-retention yielding unprecedented diastereomeric excesses, as high as 70%, in the recombination of the radicals to form meso- and (+ )-succinodinitriles (Brittain et al., 1984). When the methyl esters of the diazene surfactants were decomposed in a chlorobenzene solution, poor diastereoselectivity was observed, diastereomeric excesses of 2.6% and 7.4% for meso- and ( )-isomers respectively, which is typical of free radical processes in isotropic media (Greene et al, 1970). 

Benzene, toluene, ethylbenzene and chlorobenzene have been shown to be suitable substrates under these conditions, and the reaction rates are 50 to 70 times faster than for uncatalysed reactions. This reaction can be further enhanced by use of methanol as a co-catalyst, which allows bromination of anilines in quantitative yield with complete selectivity for the para- isomer [54],... 

Interesting examples of a tandem Cope-Cope rearrangement are represented by the transformation of Cookson s diester 499, which proceeds thermally to afford its ring-degenerate isomer 500 (330-350 °C, as a melt) (equation 188)246, and by thermal isomerization of bicyclic triene 501 into hexahydro-1-vinylnaphthalene 502 upon heating in chlorobenzene at 220 °C for 20 h (equation 189)247. 

The isomeric effect of the AAH value of substituted chlorobenzenes was very small. This means that the molecular size of the isomers is almost the same however, the actual size is not the same under these chromatographic conditions.38... 

Seddon and coworkers studied the Friedel-Crafts acylations of toluene, chlorobenzene and anisole with acetyl chloride in [emim][Al2Cl7] and obtained excellent regioselectivities to the para isomer, Scheme 9. Similarly, the fragrance chemical, traseolide, was obtained in 99% yield as a single isomer. Scheme 10. It should be noted, however, that the question of product recovery from the reaction medium still needs to be addressed in these systems. 

Decomposition of 3,4,5,6-tetrachlorobenzene-2-diazo 1-oxide (68, Scheme 17) in chlorobenzene at 130°C presumably involves the ketocarbene 69 and yields some of the dibenzofuran 72 via the 2 -chloro-2-biphenylol 71 because its isomer (70) is also a product. 

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